Answer: (D) IgG

IgG is the most abundant immunoglobulin in human serum, comprising 75-80% of total antibodies. This makes it the correct choice for competitive exams like CSIR NET Life Sciences.

Option Analysis

• (A) IgM: First antibody produced in primary immune response; pentameric structure; 5-10% of serum immunoglobulins.​

• (B) IgA: Predominant in mucosal secretions like saliva and tears; second most common in serum at 10-15%.​

• (C) IgD: Present in trace amounts (0.2-0.25%); mainly on naive B cell surfaces; minimal serum role.​

• (D) IgG: Monomeric; crosses placenta for fetal immunity; dominates serum at 75-80% concentration (8-16 mg/mL).​

Serum Abundance Table

The most abundant immunoglobulin in serum is IgG, accounting for 75-80% of total antibodies and playing a central role in long-term immunity. This fact is crucial for understanding humoral immunity in molecular biology and CSIR NET preparation.​

Immunoglobulin Classes Overview

Human serum contains five main immunoglobulin classes: IgG, IgA, IgM, IgD, and IgE, distinguished by heavy chains (γ, α, μ, δ, ε). IgG’s monomeric structure (150 kDa) enables wide distribution in blood and tissues.​

Why IgG Leads in Serum

IgG provides secondary immune responses, opsonizes pathogens, and activates complement effectively. Its half-life (21 days) sustains high levels (8-16 mg/mL), unlike larger IgM (900 kDa, intravascular only).​

Comparing Other Classes

• IgA (10-15%): Protects mucosal surfaces; dimeric in secretions.​

• IgM (5-10%): Pentameric; excels in primary responses via high avidity.​

• IgD (<0.3%): B cell receptor; limited serum function.​

• IgE (trace): Mediates allergies and parasites.​

Exam Relevance for CSIR NET

Questions on “most abundant immunoglobulin in serum” test antibody distribution knowledge, vital for immunology sections. Memorize percentages: IgG > IgA > IgM >> IgD/IgE.​